A variety of expandable intraluminal medical devices have been developed over recent years. For example, stents are routinely used in several body lumens as a means for providing support to ailing vessels, such as coronary and non-coronary vessels. Occlusion devices are used to substantially block fluid flow through a body vessel, and prosthetic valves are used to regulate fluid flow through a body vessel. Both prosthetic heart valves and venous valves have been the subject of significant development efforts in recent years.
Expandable intraluminal medical devices are typically delivered to a point of treatment using a delivery system designed for percutaneous techniques. In a conventional delivery procedure, a caregiver navigates the delivery system through one or more body vessels until the expandable intraluminal medical device, which is typically contained in a distal tip of the delivery system, is positioned at or near the desired point of treatment. Next, the caregiver deploys the expandable intraluminal medical device from the delivery system, either by removing a constraining force for self-expandable devices or by providing an expansive force for balloon-expandable devices. Once deployment is complete, the delivery system is removed from the body vessel, leaving the intraluminal medical device in an expanded configuration at the point of treatment. This delivery and deployment technique is largely conventional and is used for most types of expandable intraluminal medical devices, including stents, occluders, valves, and other types of devices.
During delivery, expandable intraluminal medical devices are maintained in a compressed or reduced-diameter configuration within the delivery system to ensure navigability of the delivery system through the body vessel. Generally, delivery systems for implanting expandable intraluminal medical devices in body vessels include a sheath placed over a dilator or other elongated member. The expandable intraluminal medical device is disposed on the dilator, between its outer surface and the inner surface of the sheath. The sheath provides the constraining force that maintains self-expandable intraluminal medical devices in the compressed configuration. Following navigation of the delivery system to a point of treatment in a body vessel, the sheath and/or dilator are moved relative to each other to remove the constraining force of the sheath, allowing the intraluminal medical device to deploy. Self-expandable devices transition to the expanded configuration simply by removal of the constraining force, which other types of expandable intraluminal medical devices, such as balloon expandable devices, require the application of an outwardly-directed radial force, such as by inflation of an underlying balloon, to achieve their expanded configuration.
The relative movement between the sheath and dilator during deployment results in friction between the interior surface of the sheath and the exterior surface of the intraluminal medical device. Extensive friction can be disadvantageous for a variety of reasons. For example, it may cause the intraluminal medical device to move relative to the dilator as the sheath or dilator is moved, which may result in deployment of the intraluminal medical device at a point that is spaced from the intended point of treatment. Even a slight spacing from the intended point of treatment can be disadvantageous for certain types of expandable intraluminal medical devices and/or certain clinical situations, such as deployment of stents at a plaque site within a body vessel, deployment of a valve at a desired valving location, and deployment of a stent-graft device at a desired exclusion site in a body vessel. The friction between the interior surface of the sheath and the exterior surface of the intraluminal medical device also creates the possibility for damage to the intraluminal medical device. For example, several intraluminal medical devices include a graft member or other attached component. Friction between the sheath and the underlying device may increase the likelihood that the graft will crease, tear, or even detach from the associated support frame during deployment. Furthermore, such friction could disrupt localized bioactive deposits that are associated with the support frame, graft, or other attached member, such as localized deposits of a therapeutic that are intended for contact with a specific portion of the body vessel wall.
Thus, there is a need for medical device delivery systems that provide advantageous frictional properties between the sheath and the underlying expandable intraluminal medical device during deployment of the medical device at a point of treatment in a body vessel.